I think someone explained that only browsers and maybe some applications check the CT logs in the first place. Most applications don't, so someone can impersonate any URL an application connects to and the attacker doesn't have to publish to a CT log.
replyHow would certificate transparency logs have helped here though? If the private key leaks and anyone can mint a valid certificate that gets accepted, those logs aren't going to reveal it.
replyIf an attacker takes the CA key and issues a valid certificate, but does not log it to CT, mainstream browser clients will not accept it.
replyWhen a certificate is logged to CT, you get back an SCT, and the issuing CA will normally include that in the certificate. The browser will then accept this certificate as it has the correct SCTs (there are always at least two).
The attacker issued certificate hasn't been logged, so can't have an SCT, so won't be accepted by the browser.
We can't say that no certificates have been issued by an attacker. We can say that no certificates have been issued by an attacker that a modern browser client would accept.